Allow setting of allowInsecure for scrapers in web interface

[gg-g]

Context
InfluxDB 2.0.6

Proposal:
This fix added the option to allow skipping of certificate checks for self-signed certificate on HTTPS scrape targets. At the moment this can only be set via the API.

Add a checkbox to the InfluxDB WebUI to set this for convenience.

Current behavior:
Adding a HTTPS scrape targets which has a self-signed certificate or certificate issued by a private CA can be done and is marked with all green check-marks. In the log however, it warns about certificate issues:

ts=2021-05-28T15:43:32.679772Z lvl=error msg="Unable to gather" log_id=0UK~I9il000 error="Get \"https://influxdbhost.example.com:8086/metrics\": x509: certificate signed by unknown authority" ts=2021-05-28T15:43:42.677452Z lvl=info msg="http: TLS handshake error from 10.0.0.218:58118: remote error: tls: bad certificate" log_id=0UK~I9il000 service=http

Desired behavior:
A checkbox in the Create Scraper dialog that sets allowInsecure on the scrape target

Alternatives considered:

Use case:
Why is this important (helps with prioritizing requests)?

Convenience :)